The invention is directed to a boriding agent for boriding mass produced parts of ferrous and non-ferrous metals, the boriding agent comprising a boron yielding (or imparting) material, activator, filler and binder.
The boriding of iron materials and non-ferrous metals has been known for a long time as a process for producing wear-preventing coatings. Of the processes described in the literature until now there has only been able to be reduced to practice to a significant extent the powder boriding process. In this process the production part to be treated is packed into a mixture of different materials and subjected to a temperature treatment. As the boriding agent for the most part there is used a mixture which consists of boron carbide as the boron yielding substance, silicon carbide or another filler for regulating the activity and potassium borofluoride as the activator. This mixture furthermore contains in part amorphous carbon and other additives which should increase the activity. It is used as a powder or granulate. The temperature treatment is carried out nearly exclusively in oven furnaces, muffle furnaces or pot furnaces.
Although trouble-free boride coatings are produced by these procedures, they have several severe disadvantages. The packing of the production pieces in the boriding agent and the unpacking are only possible by hand. The area of use of the process from the beginning is limited to the treatment of individual pieces or small series. However, the process is only used reluctantly in practice with large or complicated shaped individual pieces since the consumption of boriding agent is very high in thoses cases. Finally, the partial boriding, i.e., the treatment of separate parts of the production pieces is either impossible or is only possible with considerable difficulty.
For these reasons there has not been a lack of attempts to bring the boriding agent into a brushing, spraying or dipping consistency. Thus the pulverulent boriding mixture is treated with water (e.g., German OS 2147755) whereby a certain binding is effected through the soluble salt-like components of the boriding agent. Also, there has been recommended the use of organic binding agents, as, e.g., acrylic resins, dissolved in acetone (German OS 2361017).
In using pastes the treatment is advantageously carried out under a protective gas (e.g., hydrogen, forming gas) or in a vacuum. The boride coatings therethrough become more homogeneous in regard to their structure and their thickness.
The described boriding pastes until now have had no significant use in practice since they do not fully satisfy the established requirements. Thus, there is the disadvantage that the previously proposed pastes are inclined to separate into their components, i.e., the specifically heavier constituents such as boron carbide and silicon carbon settle to the bottom. Besides, especially with pastes produced with the organic binders and solvents the danger of fire plays an important roll. Finally, with complicated shaped production pieces it is difficult to remove the residual paste without trouble. Also, the use of ultra-sound in this event does not lead to satisfactory results in all cases.
Therefore, it was the problem of the present invention to find a paste for boriding mass produced parts of ferrous and non-ferrous metals which can be applied by brushing, spraying or dipping and which does not have the disadvantages pointed out above. It should be especially stable in storage, non-flammable and easily removed from the production pieces. Furthermore, this paste should be able to be used to make possible a continuous process for boriding a large series of small parts.